Effects of pore structure on the moveable oil saturation in water-driven tight oil sandstone reservoirs
Effects of pore structure on the moveable oil saturation in water-driven tight oil sandstone reservoirs
复制标题
水驱致密油砂岩储层孔隙结构对可动油饱和度的影响
DOI：
10.1016/j.petrol.2021.109142
复制
发表时间：
2021-06-27
影响因子：
--
通讯作者：
Shao, Longkan
中科院分区：
文献类型：
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作者：
Liu, Hongping;Luo, Yang;Shao, Longkan
致密砂岩油藏储量大，但水驱油效率低，采收率低。可动油饱和度是评价水驱致密砂岩油藏采收率的重要参数。然而，其在致密油砂岩中的控制因素仍然没有得到很好的理解。在这项研究中，在鄂尔多斯盆地（中国）红河油田长8和长9段的致密/低渗透砂岩提供了一个机会，以确定孔隙结构对MOS的影响。采用孔隙度、渗透率、薄片、扫描电镜（SEM）、大视场扫描电镜成像法（MAPS技术）、高压压汞（MICP）、显微CT扫描等方法，系统分析了储层的孔隙结构。MOS值从相对磁导率测试中获得。结果表明，孔隙度、孔喉尺寸和分选系数与MOS值之间没有明显的相关性。许多高磁导率样品甚至显示出较低的MOS值。此外，注水前后的微CT图像分析表明，低渗透率样品往往比高渗透率样品扫描更大的区域，从而导致更大的驱油效率和MOS值。而压汞曲线顶点处的累积汞饱和度（S apex）、最大孔喉半径与中等孔喉半径之比（R-max/R-50）、可动流体饱和度（MFS）与MOS呈现良好的线性关系。驱替油主要来自粒间孔隙，部分来自粒内孔隙。在颗粒与颗粒接触面上广泛分布的微孔，原始含油饱和度低，驱油效率低。提出了无论岩石类型如何，对渗透率有贡献的连通孔隙的体积是控制MOS的关键因素。
Tight oil sandstones have large oil reserves but low waterflooding efficiency and oil recovery. The movable oil saturation (MOS) is a critical parameter for evaluating oil recovery in water-driven tight oil sandstone reservoirs. However, its controlling factors in tight oil sandstones are still not well understood. In this study, the tight/low-permeability sandstones in the Chang 8 and Chang 9 Members of the Honghe Oil Field in the Ordos Basin (China) provide an opportunity to determine the effects of pore structure on the MOS. Porosity, permeability, thin sections, scanning electron microscopy (SEM), large field-of-view SEM imaging method (MAPS technique), highpressure mercury intrusion (MICP), and micro-CT scanning were systemically conducted to analyze the pore structure analysis. MOS values were obtained from the relative permeability tests. The results show that porosity, pore-throat size, and the sorting coefficient have no evident relationship with the MOS. Many of the higher-permeability samples even show lower MOS values. Moreover, analysis of micro-CT images before and after waterflooding indicates that the lower-permeability samples tend to swept larger areas than the higher-permeability samples, resulting in greater oil-displacement efficiencies and MOS values. Instead, the cumulative mercury saturation at the apex of the mercury injection hyperbola curve (S apex ), the ratio of the maximum pore-throat radius and the medium pore-throat radius (R-max/R-50), and movable fluid saturation (MFS) show a good linear relationship with the MOS. The displaced oil is primarily from intergranular pores and partly from intragranular pores. The micropores that are widely distributed at the grain-grain contact display low original oil saturation and low oil displacement efficiency. It is proposed that the volume of the well-connected pores that contribute to permeability is the key factor controlling the MOS regardless of the type of rock.